Hi - I have taken a few days to really think about your question: can Yin Yoga help with spondylolysthesis? I have to admit, I am not sure. I have not heard of any non-surgical ways to realign the spine when a disk has slipped over top of the lower disk or sacrum (usually due to a crack in the bone structure between the two disks). Normally, interventions for spondylolysthesis relate to pain management and regaining normal mobility, rather than fixing the "problem." It sounds like you want to go further than that and actually fix the disks.
In my experience, severe spondylolysthesis does seem to occur in very flexible people. I know of one woman who has it and she was a high level gymnast and dancer with a good deal of flexibility. It is her experience that I would like to relate to you. She has been doing yoga for decades but neither yin yoga, nor any yang forms of yoga seemed to help her condition. Over the last year she has made significant progress is realigning her spine, not through physical yoga but through guided meditation!
Normally I would be skeptical that meditation could help with spondylolysthesis, but I can palpate her lumbar spine and the change over the last year is quite amazing. I can't guarantee that you will have the same improvement, but it may be worth trying.
Her meditation basically is as follows:
- Feel your lower back and feel energy flowing up and down the spine
Imagine your vertebrae coming into alignment and feel the energy flowing freely
Picture your spine straightening - try to feel what this would feel like
Make these feelings and pictures as vivid and real as you can
Keep doing this, everyday for 10 minutes or more each day.
Yin Yoga works the deep connective tissues to make them thicker, stronger and healthier, but to help realign your slipped vertebrae may require a deeper stress to this area than normal poses can deliver, and the stress may make the spondylolysthesis deepen rather than lessen. Before doing more yoga poses, make sure your physio or health care professional is onside with it.
The idea would be to slide the L5 vertebrae back "out" while pushing the sacrum "in". Butterfly could move the L5 backwards but it also pushes the sacrum backwards. Seal pose could push the sacrum in, but it also pushes the L5 in. It is difficult to isolate the sacrum from the L5 and move these two bones in opposite directions, which is why I am not sure that Yin Yoga or any generic yoga can help you.
However, try the meditation that my friend has been doing and see if this can work the same miracle for you that she has been experiencing. Let us know how it goes.